Effect Of Strong Deformation Rolling Process On Microstructure And Properties Of Mg-6Sn-3Al-Zn Alloy

As the lightest metal structural material in practical engineering applications,magnesium alloy has been widely used in aerospace,3C products and transportation.The rolling process of magnesium alloy sheets,especially the research of strong deformation rolling,is immature,which limits the widespread application of magnesium alloy sheets in other fields such as environment,energy and information.In this paper,Mg-6Sn-3Al-Zn alloy was used as the research material,and the traditional rolling process and the pack rolling behavior of high reduction rate were studied.In this paper,Mg-6Sn-3Al-Zn?wt.%?alloy was prepared by using CO₂ and SF₆gas protection in the crucible furnace.The experimental equipment we used include BKD?150×260 experimental rolling mill,Instron-5982 universal testing machine,Leica DMI3000M optical microscope,X-ray diffractometer?XRD?and scanning electron microscopy?SEM?,etc.These devices had been used to observe and analyze the microstructure,room temperature tensile properties and macroscopic texture of as-cast alloys and two as-rolled alloys.The microstructure of the as-cast Mg-6Sn-3Al-Zn alloy is mainly composed of matrix?-Mg and a large number of uniformly distributed Mg₂Sn phases.The Mg₂Sn phase mainly distributes at the grain boundary in strips or granules,and some of the particles are distributed inside the grain;the tensile strength,yield strength and elongation of the as-cast alloy are 207.0MPa,88.7MPa and 12.7%,respectively.In the two rolling experiments of traditional rolling and high reduction rate pack rolling,the effects of rolling temperature and rolling deformation on the microstructure and properties of the alloy were investigated.In order to study the effect of temperature on the structure and properties of TAZ631 alloy more accurately,in the conventional rolling temperature experiment design,the temperature difference of 100?was used to determine the optimum rolling temperature,and then the temperature difference was reduced to study the high reduction rate pack rolling.It is known from the literature that the pack rolling can effectively reduce the rolling edge cracking,and the high reduction rates rolling experiments of two passes,23%per pass?sumup 40%or so?,two passes,35%per pass?sumup 60%or so?and two passes,55%per pass?sumup 80%or so?were tried.Two rolling tests shown that the change of rolling temperature and deformation affect the surface quality of the rolled plates.The number of edge cracks decreased with the temperature increased and the rolling reduction decreased.Compared with the conventional rolling,the surface quality of the magnesium alloy sheets rolled by the 6063 aluminum alloy sleeve was better overall.In particular,the rolling plate with a single pass reduction rate of 55%and a cumulative rolling reduction rate of80%for two passes had a side cracking condition similar to that of a conventional rolling multi-pass cumulative reduction ratio of 80%.The pack rolling can effectively improve the rolling quality of the sheet.The metallographic microstructure of the TAZ631 alloy after rolling deformation was observed.When the traditional rolling test was carried out at low temperature,the alloy did not undergo dynamic recrystallization,twin crystal structures existed,and the as-cast equiaxed crystal become a deformed grain elongated in the rolling direction during the rolling process.With the rolling temperature and reduction rate increased,the recrystallized structure increased,resulting in the formation of a mixed structure with large and small grains were unevenly distributed.After rolling with high reduction rate,the structure was further refined,and"necklace"structure was formed when rolling at 350?.When the rolling reduction ratio increased to 80%,high density recrystallized structure were formed around the larger crystal grains,and the morphology of a bimodal distribution of large crystal grains and small crystal grains was formed.The macroscopic texture of Mg-6Sn-3Al-Zn alloy sheet under different rolling conditions was studied.After rolling,the strongest peak of X-ray diffraction changed from the as-cast{101^—1}to{0002}crystal plane,and the alloy sheet formed a apparent{0002}base panel texture.The Base texture strength decreased with the temperature increased and the rolling reduction decreased.After deformation by two rolling processes,the tensile properties of the alloy sheet at room temperature in the RD direction were greatly improved.After comprehensive analysis,the optimized rolling parameters of Mg-6Sn-3Al-Zn magnesium alloy were as follows:6063 aluminum alloy sleeve rolling,rolling temperature:450?,reduction rate:55%-55%?cumulative deformation:80%?.For this condition,the tensile strength,yield strength and elongation were 325.99MPa,211.55MPa and 20.6%,respectively,which were 57.5%,138.5%and 62.2%higher than the as-cast state,respectively.While maintaining elongation,the tensile strength,yield strength were 11%and 13.7%higher than that of the optimum sample by conventional rolling,respectively.